The invention relates, generally, to LNG powered vehicles and, more particularly, to a relief valve jet to minimize the ignition hazard from such vehicles.
In recent years numerous advances have been made in developing alternative fuels for powering vehicles. One alternative fuel, liquified natural gas (LNG), has proven to be one of the more promising and widely accepted alternative fuels and is presently being tested and used on vehicles such as city bus fleets.
The use of LNG as a motor vehicle fuel has numerous advantages over gasoline and other alternative fuels. LNG is low cost, clean burning, widely available domestically, non-contaminating in spills and has a high energy density and high ignition temperature. One problem with LNG is that it is a cryogenic liquid, i.e., a gas that exists as a liquid only at extremely low temperatures. As a result, if a fuel tank filled with LNG is allowed to sit without being used, heat will be transferred to the LNG causing it to vaporize and build pressure in its tank. To regulate the pressure in the tank the vaporized natural gas is eventually vented to the atmosphere. As a result, vehicles that are powered by LNG include a vent stack for venting the vaporized natural gas to the atmosphere.
While venting itself is not hazardous, natural gas is highly flammable and presents a fire hazard at the vent stack where open flames or sparks in the vicinity of the vent stack can ignite the venting gas. Additionally, there is the possibility, when venting indoors, for example in bus terminals, for the methane rich natural gas to pool at the building ceiling and be ignited by lights or ventilators. Obviously, these conditions present an undesirable safety hazard.
Thus, an improved vent system for LNG powered vehicles is desired.